Astronomers have announced a whole new passel of planets orbiting stars near the Sun: 50 more, the single largest group ever announced at one time*. It’s an indication of just how good we’re getting at finding these things. Even better: many of these planets are at the upper end of what we might call Earth-like.

The instrument, called HARPS, for High Accuracy Radial velocity Planet Searcher, is a spectrograph. It takes light from distant objects and breaks it down into incredibly thin slices of wavelength, like a rainbow with a hundred thousand colors†. A planet orbiting a star tugs on the star with its gravity, pulling it toward and away from us over the course of its orbit. This makes an incredibly small shift in the colors of the star, but well within the capability of HARPS to detect.

The team used HARPS (PDF) to survey 376 stars like the Sun (similar mass, size, and temperature) and found that 40% of them have at least one planet with less mass than Saturn. 40%! That’s incredible! Just doing some very rough math, 10% of the stars in the Milky Way could easily be called Sun-like. If 40% of those host planets the size of Saturn or smaller, there are billions of planets that size in our galaxy alone.

That’s a whole lot of planets.

They also found that Neptune-mass planets appear to be common in multiple planet systems; in fact that’s apparently where the majority of them are. In other words, planets like Neptune are pretty easy to make, especially when there are other planets in the system.

16 of the 50 planets discovered by HARPS in this release are so-called "super-Earths", with masses a few times that of our home planet. Interestingly, you might expect them to have higher gravity than Earth since they’re more massive, but if they are also less dense — that is, bigger in size — then you might not weigh all that much more standing on the surface of one. For example, a planet with 5 times Earth’s mass but twice the radius would have a surface gravity only 20% higher than Earth; if you weighed 150 pounds here you’d weigh 180 pounds there.

Unfortunately, HARPS can’t tell us the sizes of these planets, just their masses — the planet would need to transit its star for us to get that information. We also have no clue if these planets have atmospheres or, if they do, what they’re made of.

However, it can tell us how far these planets are from their stars, and given the temperatures of the stars involved, we can also state that two of these super-Earths (Gliese 851 d and HD 85512b (PDF)) are near or inside the zone around their parent stars where liquid water could conceivably exist on their surfaces. Again, we don’t know a whole lot about these planets just yet except their masses, but their location at the right distances from their stars is a good sign. It means there could be a whole lot of planets out there that look a whole lot like Earth.

And we’ll know better very soon. A new exoplanet-finding instrument is being built and will be operational in 2016. Called ESPRESSO — Echelle SPectrograph for Rocky Exoplanet and Stable Spectroscopic Observations — it’s an even more sensitive instrument than HARPS. It should be able to detect the planets with the same mass as Earth, well within their stars’ habitable zones. From another star, it could actually detect Earth orbiting the Sun!

When I was learning about the Solar System as a kid ,from every book on Astronomy I could get my hands on ,Other Solar Systems were just a theory . Most of the books at that time said there might be planets orbiting other stars, but it has not been confirmed. now 50 years later we haved confirmed that other stars have planets.I think this shows how far Astronomy has come in 50 years ,who knows what we will find in another 50 years.

#3 NCC-1701-Z , This is not what you have to worry about . The real threat is seed pods form one of thoese planets comeing to Earth and makeing copys of us while we sleep so we go to the polls and vote Anti-Science . THERE COMING , THERE HEAR ALLREDY YOULL BE NEXT!!!!!!!! AAAAAAAAAAAAAAAAAAAA!!!Just kiding , I don’t think weve found life on these planets yet. But there could be.If so we are not alone.

When I was a child, enthusiastically reading about the stars and planets, I could have fathomed the possibility of other worlds… but it would have just been speculation, wild speculation. And now, not only do we have confirmation of their existence, but it’s plausible that they might also be Earth-like. We could potentially go there, and live there.

And we’re just getting started. Detection methods and data analysis will improve every year as we push the limits of our technology and ingenuity.

I would have liked to have seen Neil and the gang land on the Moon, and I often sigh sadly that I cannot live those moments… but looking forward, what a marvelous universe is stretched out before us, and every day we wade deeper into it. What a time to be alive.

I don’t know where in relation they would all be. You can probably check the Wiki entry for that. However, plotting their positions on a map would be problematic; Gliese 851 d, for example, is 20 light years away. The Milky Way is 100,000 light years in diameter, give or take a Kessel Run. Most of these planets are within that range; a few dozen light years, or about 0.0002% of the diameter of the galaxy. This means, if you were to shrink the Milky Way down to the size of a ruler, most of these planets would be within one thousandth of an inch.

*… takes a moment to check his math*

Wow.

EDIT: Ok, I checked out the Wiki page for stars with extrasolar planets:

If you sort the list by increasing distance, and then scroll down to WASP-6 at 1002 ly, everything above that point, on our Milky Ruler, would be within 1,000/100,000 of an inch, or 0.01, or one-hundredth, or approximately one third of one thirty-second. So take the smallest increment on your average ruler, the one-thirty-second increment, divide it into thirds, and one of those would be where all those stars are. Just shy of 90%, by my count.

Just curious. In general, how does the angle of line of sight figure in? If our line of sight is perpendicular to the planet’s orbital plane, then we would not be able to detect shift in wavelength of light from star caused by to the gravitational effect of a planet on a star, right? So angle can be 0-90 degrees, how does this factor in to derive a planetary mass and orbital radius?

@#5 Nobilis Reed. One thing thatmost people forget about the “great silence” is the pesky inverse square law. Our own civilization is barely detectable outside the orbit of Pluto with the Arecibo! A directed (or beamed) message would of course exceed that distance, but if you think about us as humans, he have only done that maybe a dozen times. And then the recipient has to be listening at just that time, with the appropriate technology.

Add to all this, we are actually decreasing the leakage of radio signals to space as we go to more fiber communication, and precise focusing of our transmissions.

I don’t think that the great silence is a big mystery, but disappointing none the less. One step at a time though.

Well I always said there had to be hundreds of thousands at the very least in our galaxy alone, but a bunch of idiots continue to believe to this day that Earth is the only one. Clearly they have no common sense, and it’s reasons like that, I do not belive their religious nonsese either.

There’s earthlike and then there is reality- much of what makes our planet the way it is is not just down to size and distance from the sun but also the effects of the impact that created the moon. Having an axis stabilizing moon is nice, and tides are good too, but the composition of the earth had to have changed after impact. We ended up with more radioactive metal in the core, and less of the rocky stuff relatively (the moon is the other way round). More metal, more plate tectonics for lots longer, so more mountain building, and all sorts of nice element cycles that help keep us alive (and perhaps made us in the first place). An ‘earth’ without a large moon may be more like Mars or Venus, though in a larger body the scaling-up may enhance tectonic processes. Thus we may be one of the only smallish planets out there capable of supporting life- others have suggested this as well. A nice low-pressure existence! So when they come in their ships and call us Puny Earthlings, maybe the planet is being insulted, not necessarily ourselves.

This is great, amazing, wild, wacky stuff. But even if we do find several candidates, it begs the question: How the hell will we get there? The farthest man has been able to send anything so far has been Voyager 1, which after 30-odd years is a mere ~0.001 Light Years away. I can only hope that any discovery will rekindle our desire to explore, be it by robot or human.

Every planet in our SS Venus sized or larger has a thick atmosphere, so it stands to reason that all planets w/ sufficient mass will have gravity bound volatiles as a result of their formation. The constituents of such atmospheres is unknown, but nitrogen and carbon dioxide are leading contenders for terrestrial planets. Oxygen is rare unless there is life I would guess.

The paper makes further reference to the situation with Gliese 581, they say they are now able to rule out the existence of planets f and g (a somewhat stronger statement than when they originally stated they were unable to confirm these), more details in a forthcoming paper.

Well, consider that the odds in our own solar system of sustaining life are pretty low.

Mercury, Venus, Earth, the Moon, Mars, several moons of Jupiter, Saturn, etc, all are solid, some have atmospheres, only one supports much life. Mercury gets fried, Jupiter’s moons are irradiated by it’s massive field, Saturns are frozen, Mars atmosphere disappeared, and Earth has been nearly destroyed by nuclear war on several occasions, often averted only by accidents or the decisions of a single person. It has also been hit be mega-asteroids. And nobody knows exactly what happened to Venus, but it sure wasn’t good.

@12. James Nelson:
“In general, how does the angle of line of sight figure in?”

Quite a lot. What HARPS measures is v sin(i), which means the masses they get out are m sin(i). The mass could be anywhere from the number they give in press releases (if i=90, sin(i)=1 aka directly in the line of sight) to stellar-mass (if i~0, sin(i)=big). As Phil says, the only way you’ll know the mass well is if the planet also transits, because a transit requires i~90.

There is a lot of work being done following up transiting planets to get their radial velocities, because you know it’s there, and you can get the mass. On the other hand, the transit surveys miss TONS of planets that didn’t just happen to line up at nearly 90 degrees inclination. Take that 1200 number Phil quoted and multiply it by… oh, a lot.

@12 James Nelson: Digital Axis beat me to it — the actual mass of the planet could be slightly higher than the published value, or two times, or twenty times, depending on the inclination of the orbit. Generally, the only upper limit on the planet’s mass comes from the fact that we don’t observe it directly — so we know it’s not star-sized! Personally, I think all of the mass-period plots should use little upward arrows to avoid forgetting this important issue, but I admit that arrows make for cluttered plots.

@26. decora
“the odds in our own solar system of sustaining life are pretty low. ”

Life we’re familiar with, perhaps. But then there’s bacteria like the ones they found in a gold mine in Africa (click my name). It is, apparently, its own self-supporting web of life, and I’m not sure if it relies on oxygen to survive. Drop it into the right environment underneath the surface of Mars and it could happily live there right now. Well, you’d apparently need liquid water…

Congratulations & thanks to the astronomers and people involved in making this marvellous discovery and can’t wait tohear more on these new found worlds.

The team used HARPS (PDF) to survey 376 stars like the Sun (similar mass, size, and temperature) and found that 40% of them have at least one planet with less mass than Saturn. 40%! That’s incredible! Just doing some very rough math, 10% of the stars in the Milky Way could easily be called Sun-like.

How similar to the Sun is “Sun-like” and similar though?

Only about 4% of stars belong to spectral type G – our sun’s yellow dwarf class. About 15 % are ornage dwarfs of type K and of them many might be pushing the too small and thus dim boundaries whilst far fewer are type F the hotter end (earlier than about F5) are probably too massive, bright and thus short-lived. How exactly are we defining “Sun-like” here – main-sequence spectral classes F6-K5 or so? With certain metallicities, ages, etc .. to be considered as well? BA? Anyone?

16 of the 50 planets discovered by HARPS in this release are so-called “super-Earths”, with masses a few times that of our home planet. Interestingly, you might expect them to have higher gravity than Earth since they’re more massive, but if they are also less dense — that is, bigger in size — then you might not weigh all that much more standing on the surface of one. For example, a planet with 5 times Earth’s mass but twice the radius would have a surface gravity only 20% higher than Earth; if you weighed 150 pounds here you’d weigh 180 pounds there.

Pretty sure I read somewhere that Neptune’s “surface” gravity is about one gee – depite that azure gas giant having no less than seventeen times Earth’s mass. Is that true or false – can anyone confirm or correct that please?

How exactly are we defining “Sun-like” here – main-sequence spectral classes F6-K5 or so? Only about 4% of stars belong to spectral type G – our sun’s yellow dwarf class. About 15 % are orange dwarfs of type K and of them many might be pushing the too small and thus dim boundaries whilst far fewer are type F the hotter end of that class (earlier than about F5) are probably too massive, bright and thus short-lived. With certain metallicities, ages, the presence or absence of companion stars, etc .. as factors to be considered as well?

BTW. A good if somewhat old source and discussion of how spectral types affect the possible existence of habitable planets is for this :

Albeit it is now perhaps a bit dated. Both are still well worth reading though In My Humble Opinion Naturally.

Info. in comment #35 is from there & also from :

Croswell, Ken, “Is there Life around Alpha Centauri?” an article published in ‘Astronomy’ magazine, April 1991, Kalmbach publishing Co. which I’d also highly recommend if folks can find a copy somewhere.

On The Other Hand, red dwarfs are often flare stars especially early in their history and especially if planets are required to huddle right against their stars this may be a major argument against them hosting habitable planets as well as the tidal locking complications that get introduced.

There’s also a good overview of habitable planets and the suns they may require here :

I’d say that we really we don’t know enough to say what stars can and do host habitable worlds and how various types of star can host various types of possibly habitable wrolds yet for sure although the possibilities are intriguing and full of wonder.

If only we could go and see a good sample of these planets of other stars..

The thought occurs that here is an exoplanetary bonanza well worth HARPSing on about! 😉

@30. Chris Winter :

“Then felt I like some watcher of the skies
When a new planet swims into his ken…”

Great quote thanks – who said it & what’s the source if I may ask please?

@ 5. Nobilis Reed :

What does this imply about the Great Silence?
Personally, I think it means that the conditions conducive to life may be abundant, but the conditions conducive to long-lived technological culture may be rare.

That or there is intelligent life out there and that’s *why* we’re NOT hearing from it as its delibeartely avoiding us! 😉

I do think it’s more likely that whilst life may be reasonably common –intelligent, technological lifeforms developing is exceptionally rare.

Exhibit A : The history – or rather prehistory – of our own planet. For most of the time life existed here it was microbial only. In 4.5 billion years only one species has developed high technology that we know of.

Some of the uses that high tech has been put to and some of the problems and dangers our science and industry have created eg. nuclear weaponry, Global Overheating and overpopulation provide reason for concern as well.

The Fermi paradox remains an unanswered puzzling question but that is my guess at its explanation – technological extraterrrestrial sentiences may well be very few and far between.

@19. John Fro :

Every planet in our SS Venus sized or larger has a thick atmosphere, so it stands to reason that all planets w/ sufficient mass will have gravity bound volatiles as a result of their formation. The constituents of such atmospheres is unknown, but nitrogen and carbon dioxide are leading contenders for terrestrial planets. Oxygen is rare unless there is life I would guess.

Umm .. a lot of other factors could come into play here though.

Hot SuperEarth’s and Hot Earth’s that are close to their stars would likely experience a lot of atmospheric erosian from their stellar winds. Red dwarf flares may drive off atmospheres – especially if these planets lack or have only weak magnetic fields.

A sample size of just two – Venus and Earth – Mars is much smaller -does not enable much confidence in extrapolation. 😮

However, I would also expect that most terrtestrial rock dwarf planets do have atmospheres providing they are sufficently distant from their primary sun(s).

Is it possible they are seeing something in the data that isn’t there? I do a lot of lab testing of signals and things where I’m decoding and error correcting data from some pretty noisy channels, and sometimes you can DSP out patterns that are an artifact of the processing algorithm and not the signal.

Anyone have a link to the yummy technical nitty gritties of what they are doing to “see” these planets? Some actual data sets would be way cool.

we need a lot more resources for the research for new propulsion systems that would allow interstellar travel for probes in reasonable times.

we already have and soon will have a lot more very interesting star systems to take a closer look at. the only reasonable way to do this will be with probes that reach very close to light speed. there are some interesting concepts out there but this should be one of the primary research goals for all mankind.

@gamercow I wonder if the earliest robot we will be able to send there might be nano machines. If we can make them smart and tough enough, their tiny mass might allow us to accelerate them to near the speed of light and capture snapshots of information.
By sending a continuous stream of them at short intervals we might be able to create a relay of sorts so we can get the information back to us. Even dreaming about the possibilities is exciting stuff!

Not only is it highly probable that there is a consistent relationship between the mass of planet-to-sun ratio, but also a symmetrical differentiation between A system, and Z system (a necessary diversity between such opposing poles should be implied).

But let’s not extend ourselves too far beyond what are greater priorities in sustaining Man. Like advancing technology making scalable human adaptation easier and easier to do less, we are thereby challenged to proportionally apply existing value ranges locally, as opposed to how much we project distally.

The sustainable distribution of advanced math and science locally, must take precedence on Earth First, so Space Second can be equally sustainable in exploration. This essentially means that educational systems must change to get math and science back on an upward-and-onward trajectory – BEFORE we go hastily projecting ourselves too far into space.

Pretty sure I read somewhere that Neptune’s “surface” gravity is about one gee – depite that azure gas giant having no less than seventeen times Earth’s mass. Is that true or false – can anyone confirm or correct that please?

1.14 G at Neptune’s equator. Saturn pulls 1.06 and Uranus a feathery 0.90 G. In fact, only four objects in the solar system have a higher surface gravity than earth; Neptune, Saturn, Jupiter (2.54 G) and Sol (28.02 G).

Pretty sure I read somewhere that Neptune’s “surface” gravity is about one gee – depite that azure gas giant having no less than seventeen times Earth’s mass. Is that true or false – can anyone confirm or correct that please?

Read somewhere that it turns out that due their density, the class of planets with the highest surface gravities are the terrestrial super-earths.

Which certainly has some implications for the Fermi Paradox. If the planets most likely to harbor life and thus evolve intelligent species are also the ones with the highest surface gravity, that’s going to put a bit of a crimper on nascent space program ambitions.

A trip to Alpha Centauri would require 100 times the current energy output of the world.

I do not see humans practically mounting an interstellar expedition, even to the Centauri system, before establishing a solar system spanning infrastructure with a heavily colonized presence throughout the solar system, and routinely harvesting energy well in excess of what is practically possible with only a single planet as base of operations. For an exploratory mission, the total cost of such a mission really has to be probably less than 1% of the total GDP of the initiating civilization to have much chance of even getting past the conception stage. For colonization, perhaps a bit more, if the need is urgent enough.

(The most realistic aspect of Arthur C. Clarke’s novel 3001 to me is the fact that humanity has spread throughout the Solar System, but even after 1000 years, no sustained attempts at interstellar travel have been made.)

So here’s a question. From how many exo-planets could you in theory detect the Earth using HARPS or 21st cen technology? How big is that sphere, how many exo-planets lie with in it, how many could support life and how many of those are technological civilizations equal more or less to our own?

I bet that last number is very small. Even if it is non-zero what could they do other than observe? Without FTL the galaxy could be chock full of life but with no way to leave their local solar systems.

Thank you! That is the coolest app. EXACTLY what I was looking for. It shows where we are in the galaxy and how far each discovery is away and it’s relative position. Now if I could only display this on a huge projector screen!